We have been studying F-incompatibility, a function of the E. coli F factor related to the control of its replication. Incompatibility exists between an integrated F factor and an autonomous F factor and between two autonomous F factors. In order to determine the mechanism(s) of incompatibility, we will try to isolate more inc- mutants and to analyze and map these and the mutants we have already isolated by genetic and physical methods including DNA heteroduplexing and electron microscopy. In studying incompatibility between 2 F' factors we have found that selection for the presence of both F' factors often results in fusion of the 2 F' factors to form a single genetic and physical unit. To elucidate the process of fused plasmid formation we shall use heteroduplex analysis. We also plan to isolate phi 80 transducing phages carrying inc genes. These will be used to do physical mapping of the inc region by heteroduplex analysis and to study transcription and tranlation of F DNA in an in vitro system. In addition, we will study plasmids which carry genes for the production of enterotoxin in enteric bacteria (ent plasmids) and Pseudomonas plasmids. Their relationships to other known plasmids will be investigated by heteroduplexing techniques and by testing for incompatibility between these and other plasmids belonging to known incompatibility groups.